Heterostructures of MXenes and CoN x -Graphene as highly active electrocatalysts for hydrogen evolution reaction in alkaline media

Hydrogen evolution reaction (HER) plays a vital role in renewable energy conversion for the development of hydrogen-based energy sources. Lately, heterostructures through hybridizing MXenes with two-dimensional materials have been successfully fabricated and attract much attention due to the exceptional performance as electrodes for Li ion storage and electrocatalysts for HER. Herein, we constructed heterostructures of CoN x -graphene (CoN x -G, x = 2 and 4) supported by MXenes (Ti 3 C 2 F 2 and Ti 3 C 2 O 2 ) monolayer as highly active electrocatalysts for HER. The theoretical results show that the CoN 2 -G/Ti 3 C 2 O 2 heterostructure exhibits a high performance for HER with an over-potential (Ƞ) of only 0.33 V, and the rate-limiting step is determined to be the initial water dissociation process in alkaline media. The outstanding performance of CoN 2 -G/Ti 3 C 2 O 2 is strongly attributed to the interfacial coupling between CoN 2 -G and the MXene substrate. Our finding demonstrates that the sluggish hydrogen evolution process in alkaline media can be facilitated by taking advantage of the fast charge transfer kinetics and interfacial coupling of MXenes. Graphic abstract Herein, we theoretically design and explore 2D hybrid materials of CoN x –G supported by MXene monolayers as highly active HER electrocatalysts by using first-principles calculations. The results show that the CoN 2 –G/Ti 3 C 2 O 2 heterostructure has an outstanding HER performance with ΔG H* (0.21 eV) approaching zero as well as water molecule dissociation barrier (ΔG H–OH ) of 0.30 eV in alkaline media. This exceptional performance is strongly attributed to the interfacial coupling between CoN 2 –G and the MXene substrate.